Calcium carbonate physical precipitation

The soluble form of calcium can be precipitated in the marine environment to form rock by some physical conditions such as warming of the water (carbon dioxide is less soluble in warm water than in cold water and thus calcium carbonate is precipitated), by the use of carbon dioxide by marine plants, or by alterations in the pH of water by ammonia-producing bacteria which also lowers the solubility of calcium carbonate. However, the majority of calcium carbonate deposits are formed from skeletal fragments of organisms living in the marine environment. Some of these organisms inhabit reefs but the majority float free in water. Figure 2.13 shows various shapes of shells formed by Coccolithophorides which can be spherical coccospheres some, such as dicoaster, are star shaped. 

Hostomsky, J. and Jones, A.G., 1991. Calcium carbonate crystallization kinetics, agglomeration and fomi during continuous precipitation from solution. Journal of Physics D Applied Physics, 24, 165-170. 

Although the Langelier index is probably the most frequently quoted measure of a water s corrosivity, it is at best a not very reliable guide. All that the index can do, and all that its author claimed for it is to provide an indication of a water s thermodynamic tendency to precipitate calcium carbonate. It cannot indicate if sufficient material will be deposited to completely cover all exposed metal surfaces consequently a very soft water can have a strongly positive index but still be corrosive. Similarly the index cannot take into account if the precipitate will be in the appropriate physical form, i.e. a semi-amorphous egg-shell like deposit that spreads uniformly over all the exposed surfaces rather than forming isolated crystals at a limited number of nucleation sites. The egg-shell type of deposit has been shown to be associated with the presence of organic material which affects the growth mechanism of the calcium carbonate crystals . Where a substantial and stable deposit is produced on a metal surface, this is an effective anticorrosion barrier and forms the basis of a chemical treatment to protect water pipes . However, the conditions required for such a process are not likely to arise with any natural waters. 

Surface treatment also improves adhesion to the polymer matrix and resulting physical properties. The combination of particle size and surface treatment is critical in the selection of precipitated calcium carbonate fillers to obtain desired properties. Often graded combinations of ultrafine precipitated CaC03 and larger CaC03 particles are used for optimum properties and value. 

Experimental studies of authigenic apatite precipitation. Mechanisms and rates of authigenic apatite formation in the early diagenetic environment are difficult to resolve, because of the wide variety of biological, chemical, and physical factors that can affect its formation. Experimental studies of apatite formation under controlled conditions have provided important information for placing constraints on modes and rates of CEA authigenesis. Examples of such studies include those of Ames (1959), who documented nucleation of CEA on calcium carbonate Gulbrandsen et al. (1984), who documented rates of CEA formation in seawater Jahnke (1984), who evaluated the... 

Precipitates Drugs prepared by separating particles from a previously clear liquid by physical or chemical means. Precipitation usually occurs when a hot saturated solution of an amorphous substance is allowed to cool or when a liquid in which the dissolved substance is insoluble is added to its solution. Pharmacists formerly used the process of precipitation as a convenient method of obtaining solid substances in fine particles (precipitated calcium carbonate), to purify solids (precipitated calcium phosphate), or to prepare mercury salts. White precipitate (ammoniated mercury) was first described by Beguin in 1632, a soluble double chloride of mercury and ammonium known to the alchemists as sal alembroth and sal sapientiae, respectively. Red precipitate (red mercuric oxide) was known to alchemists as hydragyrum preci-pitatum per se or precipitate per se yellow precipitate is a synonym for yellow mercuric oxide. " Preserves See Conserves. 

As a rule, however, the corrosiveness of a natural water is determined by the carbonic acid. Free, dissolved carbonic acid which can exist in the water as physically dissolved CO2 but also as H2CO3, can give the water corrosive properties towards metals and constructional materials (e.g. cement). From the point of view of development, waters are described as lime-corroding if they can dissolve calcium carbonate and thus also attack such constructional materials and corrode metals. If a water is supersaturated with calcium carbonate, it can be described as lime-precipitating and the formation of coatings in pipelines must be evaluated positively and... 

Nonblack fillers such as the precipitated silicas can reduce both rate and state of cure because of their strong physical interactions with the polar activator and accelerator chemicals. Neutral fillers such as calcium carbonate (whiting) and clays have little or no effect on the cure properties. Carbon black effects are small. 

Precipitated Calcium Carbonate Mississippi 72% M60 Slurry Typical Physical Analysis ... 

There are several gas-well fields that produce hydrocarbon gas associated with very high TDS connate waters. Classical oilfield scale problems (e.g., calcium carbonate, barium sulfate, and calcium sulfate) are minimal in these fields. Halite (NaCl), however, can be precipitated to such an extent that production is lost in hours. As a result, a bottom-hole fluid sample is retrieved from all new wells. Unstable components are "fixed" immediately after sampling, and pH is determined under pressure. A full ionic and physical analysis is also carried out in the laboratory. 

Sometimes ground marble can be used as a feedstock to make calcium oxide (quicklime). This precipitated form of calcium carbonate is finer in particle size and of a significantly higher purity and cost than the ground limestone. Still, these precipitated calcium carbonates are not reinforcing fillers in that they do not significantly improve the physical properties of the cured rubber compound. 

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